1) Field of the Invention
The present invention relates to a power supply apparatus, and particularly, relates to apparatuses where electrical power consumption can be greatly reduced. The power supply apparatus according to the invention can be suitably applied to any electrical appliance having a remote controlling system, such as television equipment, video equipment, audio equipment and air conditioning systems; electrical appliances where a sub-switch is provided to change the operational mode between a standby mode and a driving mode; electrical appliances, which should keep them in their standby mode even when the main functions of the appliance are not being used, such as telephone equipment, facsimile equipment and personal computers; or electrical appliances, such as modems and printers, which are designed such that electrical power is supplied through AC adapters.
2) Related Prior Arts
A remote controlling system is used in many kinds of electrical appliances, due to its convenience. Recently, such appliances are so designed that a main switch for turning on or off the main unit of these appliances is omitted and thus the appliances always keep their standby mode for receiving an on/off signal from the remote controller during when the main unit is not being used. Further, in some of these appliances, the main switch is omitted but a small sub-switch is equipped to switch the function mode between a standby mode and a driving mode. Appliances having a remote controlling system are always in a standby mode in order to watch and wait a remote controlling signals; and the appliances having a subswitch are also always in a standby mode so that it makes possible to put the appliance in a driving mode every time even if the main unit of the appliance is not working. Therefore, either appliances always consume some electrical power for watching and waiting for a signal even when the main units of the appliances do not work.
Telecommunication appliances, such as telephone equipment and facsimile equipment, should always keep themselves in a standby condition for telecommunication signals. Therefore, in order to keep the standby function, a certain amount of electrical power is always being consumed in these appliances. Further, in the electrical equipment using an AC adapter, even if the main switch is turned off, only the secondary side of a transformer of the AC adapter is turned off, however the primary side is always kept on. Therefore, as long as the equipment is connected to a commercial AC power supply, some wasted power, so-called "no-load loss", is always consumed in the AC adapter.
FIG. 1 is a block diagram showing a basic circuit construction of an electrical power supply for use in a typical electrical appliances, such a having a remote controlling system, a timer display, etc. an audio equipment, television and video equipment. In FIG. 1, an alternative electrical current is supplied into a main unit 102 of the electrical appliance through a commercial AC power supply input terminal 101. The main unit 102 includes a main power supply (not shown) for supplying electrical voltage and current to conduct the main functions of the appliance.
On the power supply line from the commercial AC power supply 101 to the main unit 102, is provided a switching device 103, which is operated so as to open or close the power supply line in accordance with a signal coming from a control circuit 104 for use in a remote controlling function.
In the control circuit 104, are provided an auxiliary power supply 105, a light receiving circuit 106 for receiving a remote controlling signal, a CPU 107 for outputting several kinds of control signals for driving the main unit 102, and a timer 108 for displaying a time; these elements constituting the control circuit 104 are driven by an electrical current supplied via the auxiliary power supply apparatus 105. In response to the remote control signal coming from outside, the CPU 107 sends a signal to the switching device 103 to close the circuit for supplying electrical power from the commercial AC power supply 101 to the main unit 102 and the CPU 107 also sends control signals to the main unit 102 for controlling the functions thereof.
The timer 108, which is necessary to be driven even during when the appliance is in a standby mode, is provided in the circuit 104 to drive a liquid crystal display 109 to display a time thereon. However, since a back light system 110 for the liquid crystal display 109 consumes a great amount of power, the system 110 is arranged so as not to be lit on during the standby mode but to be lit on only when the main unit 102 is in a driving mode by obtaining power from the main power supply apparatus provided in the main unit 102.
The control circuit 104 also comprises an electrical charge storing element 111, such as a capacitor, where electrical charges to maintain a standby condition of the appliance are stored. It should be noted that the initial current for operating the switching device 103 after the standby condition is released is supplied from the charge storing element 111. The current consumed in the switching device 103 at that time is filled up from the main power supply apparatus provided in the main unit 102via a diode 112.
In this manner, even in the conventional electrical appliance, some effort is paid to save the power consumption. That is to say, an auxiliary power supply is provided separately from the main power supply of the main unit, and the system, such as a remote controlling system, which needs to always be supplied with some electrical power even if the main unit of the appliance is in a standby condition is designed to be driven by the auxiliary power supply in order to save power consumption in the main unit during when the appliance is in a standby condition.
However, even if such an auxiliary power supply is provided, it is still not sufficient to save energy. Because, the apparatus, which should always be operated even when the main unit is in a standby mode, is required to be always in an electrically conductive condition, and thus a significant amount of electrical power is consumed in the apparatus.
The following four electrically conductive conditions are considered for the electrical appliance having a remote controlling function or a signal standby function or for the electrical appliance which is so designed that an electrical power is supplied through an AC adapter.
(1) Complete off condition, which means a plug for connecting the appliance to the commercial AC power source is pulled off: PA1 (2) The plug is still connected to the commercial AC power supply, i.e. inserted into the consent, but the main switch of the appliance is switched off: PA1 (3) The appliance is in a and standby condition for a remote control signal or a telecommunication signal: PA1 (4) The appliance is in a driving condition, which means the main unit is working.
Under the condition (1), there is no problem because no current goes through the appliance: under the condition (2), the appliance having a remote controlling function or the appliance which should always be in a standby condition has no problem because almost no current goes therethrough, but in the appliance using an AC adapter the above mentioned non-load loss is generated; and under the condition (3), the amount of current, which is consumed in the condition for and standby the remote control signal or the telecommunication signal, is not smaller than we expect. Because, the power supply apparatuses for use in electrical appliances are generally constructed such that only the main circuits provided in the secondary side of the transformer are switched off while keeping the circuits in the primary side of the transformer ON during the standby condition, so that some electrical current is always consumed at the primary inductance of the transformer and then so-called copper loss, which is Joule heat of the coil, and so-called iron loss, which is generated by eddy current in the magnetic cores, are generated. In the case, particularly, the power supply apparatus is arranged as a switching regulator, that a switching loss caused by the operation of a switching element is generated in addition to the copper loss and the iron loss.
In the conventional power supply apparatus or the AC adapter used in the electrical appliances, it is not enough to pay efforts to reduce such an electrical power consumption during when the appliance is in the standby condition, but more effort is being paid to decrease the manufacturing cost for the appliances by making the circuit construction simpler. However, nowadays, it should be cared to save energy from a point of view of environment on our earth, then it is becoming an important matter to save the consumption of the electrical power which is wasted when the appliances are in a standby condition.
An electrical power supply apparatus where the above problem is solved has been disclosed, for instance, in Japanese Preliminarily Patent Publication No. HEI 8-130871. The apparatus disclosed in this publication is designed as a DC-DC converter using a switching regulator; when the main unit of the appliance is in a standby mode, a switching element is controlled so as to be operated intermittently in accordance with a and standby signal in order to decrease the electrical current consumption when the main unit is in a standby mode. As stated above, however, the problem of the electrical power consumption during when the main unit is in a standby mode is not only for the DC-DC converter but also for the AC-DC converter which uses a commercial AC supply. If the technique disclosed in the above publication is applied to the AC-DC converter which uses a commercial AC supply, the following problems would be caused.
First of all, a general type of DC-DC converter is generally constructed such that an input voltage of about 24 to 48V is supplied thereinto and an output voltage of about 3 to 15V is taken from the converter. In such a converter, since the difference between the input voltage and the output voltage is small, it is available to use an initiating resister having a small resistance to initiate a control circuit for controlling the operation of the switching element. It means the power loss caused by the existence of initiating resistance is small. Contrary to this, in the AC-DC converter which uses an commercial AC supply, the input voltage is about 100V in Japan, and after rectifying the voltage becomes about 140V. In this case, since only a small amount of voltage of about 10V, which is used for driving the control circuit for controlling the switching element is taken from such a high input voltage, an initiating resister having a large the initiating resistance required to initiate the control circuit. Therefore, in the AC-DC converter, a significant amount of power is consumed by the initiating resistance, so that a sufficient effect for decreasing the power consumption cannot be obtained only by the intermittent operation of the switching element.
Second, in the apparatus disclosed in the above-mentioned publication, when the operation of the switching element is conducted intermittently, the switching frequency becomes down to about several kHz so that a discordant sound is generated from the transformer. Therefore, such an apparatus would have a problem if it is applied to the appliances for private demands, such as television equipment, video equipment, etc.
Apparent from the apparatus disclosed in the above-mentioned publication, there is a conventional switching regulator using an RCC (Ringing Choke Converter) or in a certain kind of DC-DC converter, where the switching operation of the switching element naturally becomes intermittently when the load thereof becomes extremely small, depending on the design or adjustment of the circuit. In such a converter, the switching frequency comes down to several kHz when the switching operation becomes intermittently, so that a discordant sound is also generated from the transformer. Further, there is another problem that the ripple becomes great when the switching frequency comes down. In order to prevent these problems, in the conventional switching regulator using an RCC, or the conventional DC-DC converter, a bleeder resistance is provided to prevent that the operation of the switching element becomes intermittently. Therefore, in such an apparatus, much more electrical current is consumed by the bleeder resistance in addition to that a certain amount of the electrical power is wasted during when the main unit is in a standby condition.
Furthermore, another type of DC-DC converter is suggested which is so designed that the operation of the switching element is conducted intermittently in accordance with an amount of load. Generally speaking, however, to control the intermittent operation of the switching element is comparatively easy in the DC-DC converter because there is not caused a problem concerning the isolation of a transformer. Contrary to this, a strict isolation is required between the primary side and the secondary side of a transformer in AC-DC converters, and thus it is not easy to control the operation of the switching element freely in AC-DC converters.